The use of an electric motor to rotate a fan blade to create an airflow has long been known in the art. Although such fans can produce substantial airflow (e.g., 1,000 ft3/minute or more), substantial electrical power is required to operate the motor, and essentially no conditioning of the flowing air occurs.
It is known to provide such fans with a HEPA-compliant filter element to remove particulate matter larger than perhaps 0.3 μm. Unfortunately, the resistance to airflow presented by the filter element may require doubling the electric motor size to maintain a desired level of airflow. Further, HEPA-compliant filter elements are expensive, and can represent a substantial portion of the sale price of a HEPA-compliant filter-fan unit. While such filter-fan units can condition the air by removing large particles, particulate matter small enough to pass through the filter element is not removed, including bacteria, for example.
It is also known in the art to produce an airflow using electro-kinetic technique whereby electrical power is converted into a flow of air without utilizing mechanically moving components. One such system is described in U.S. Pat. No. 4,789,801 to Lee (1988), depicted herein in simplified form as FIGS. 1A and 1B, which is hereby incorporated by reference. System 10 includes an array of first (“emitter”) electrodes or conductive surfaces 20 that are spaced-apart from an array of second (“collector”) electrodes or conductive surfaces 30. The positive terminal of a generator such as, for example, pulse generator 40 which outputs a train of high voltage pulses (e.g., 0 to perhaps +5 KV) is coupled to the first array 20, and the negative pulse generator terminal is coupled to the second array 30 in this example.
The high voltage pulses ionize the air between the arrays 20,30 and create an airflow 50 from the first array 20 toward the second array 30, without requiring any moving parts. Particulate matter 60 entrained within the airflow 50 also moves towards the second electrodes 30. Much of the particulate matter is electrostatically attracted to the surfaces of the second electrodes 30, where it remains, thus conditioning the flow of air that is exiting the system 10. Further, the high voltage field present between the electrode sets releases ozone O3, into the ambient environment, which eliminates odors that are entrained in the airflow.
In the particular embodiment of FIG. 1A, the first electrodes 20 are circular in cross-section, having a diameter of about 0.003″ (0.08 mm), whereas the second electrodes 30 are substantially larger in area and define a “teardrop” shape in cross-section. The ratio of cross-sectional radii of curvature between the bulbous front nose of the second electrode 30 and the first electrodes 20 exceeds 10:1. As shown in FIG. 1A, the bulbous front surfaces of the second electrodes 30 face the first electrodes 20, and the somewhat “sharp” trailing edges face the exit direction of the airflow. In another particular embodiment shown herein as FIG. 1B, second electrodes 30 are elongated in cross-section. The elongated trailing edges on the second electrodes 30 provide increased area upon which particulate matter 60 entrained in the airflow can attach.